From nobody Tue Sep 9 22:47:41 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34122C04FE0 for ; Wed, 9 Aug 2023 23:24:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233029AbjHIXYh (ORCPT ); Wed, 9 Aug 2023 19:24:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232261AbjHIXYa (ORCPT ); Wed, 9 Aug 2023 19:24:30 -0400 Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8501F1BFB for ; Wed, 9 Aug 2023 16:24:27 -0700 (PDT) Received: by mail-pf1-x431.google.com with SMTP id d2e1a72fcca58-686daaa5f1fso243005b3a.3 for ; Wed, 09 Aug 2023 16:24:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1691623467; x=1692228267; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=2tar+fwRF9EwexnZBlGXBQ+bino7OPSUOa9FVKEDgW8=; b=qdQX3WNwo4sWt4WkjKnJ08HLG31URbRoXVf7H5AnZ3n4OTaa437cOko2jjYggYBNx3 Uqtl8hjdOaQ5sFdI1pNdsg5WlvudRipmfEHH3jC3kSBPVvsl7sDCBIi9hJH3htjd+Scj +x4lyW8BfGjDQRdW6mPcEQh967lWkyY2MfrU8iYYuoqSur4+c4vzP8UjeTWZVpmWsXTi GrPLP1dKdTJl7/hWM1px5eML9DIPSblOF40Phwg5YuT2IX5LPipDqccZemKALDv8ntos VpDwK38TgYbp1DMAPUyfGhk2yDGhNkoAIbI8xAeXULhQkWloI08NyYlwSj+DJ7tiDJ+v bzLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691623467; x=1692228267; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=2tar+fwRF9EwexnZBlGXBQ+bino7OPSUOa9FVKEDgW8=; b=iNG6k7xvRr0WtS2PN2mWTyy12W3+DqMw0d7XSG/TXsZKXvzgKzaf5XRXvP4mIzHgbq +iVNV/9ztzHCowpUhcupHtVlgzmLbhg4UNPIDXCuWadP0BQpEE4WIkwi1K8opy8lqLLl LYOTA51f22P0Ux9+4Y64CzdzlKBC22bVCiT8ZRkjXn6xBejk6vnF/DtZRTU8klWF/9R1 vwKi++TjDwmhvrXMVvMlIy2A97nGSzXTcwC0dS1Evblbdp7JScz67WqMNu9DQdXT9jED vXzqnaj5AzBp6aCYoRU/GWqwba8j5b3v3Odxwbgr4M9TgFIncolj0vgmN3wnvSchliFh dXGw== X-Gm-Message-State: AOJu0Yy1QKpRzeb6II5GvX881qehL4G65e5xC65uceOXde7auSeL+4IT fL02pNBeUSXhL8Xmhxs0W4v85A== X-Google-Smtp-Source: AGHT+IHPggFTtnxabsF/jkLvnF3G7KP5USE4CizFGjoAWFxir/OOf3x64PmOQQ970Z2IhxBU3MEknw== X-Received: by 2002:a05:6a20:12c2:b0:131:4808:d5a1 with SMTP id v2-20020a056a2012c200b001314808d5a1mr781717pzg.28.1691623467045; Wed, 09 Aug 2023 16:24:27 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id l18-20020a170902d35200b001b54d064a4bsm82765plk.259.2023.08.09.16.24.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Aug 2023 16:24:26 -0700 (PDT) From: Charlie Jenkins To: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Cc: charlie@rivosinc.com, conor@kernel.org, paul.walmsley@sifive.com, palmer@rivosinc.com, aou@eecs.berkeley.edu, anup@brainfault.org, konstantin@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mick@ics.forth.gr, jrtc27@jrtc27.com, rdunlap@infradead.org, alexghiti@rivosinc.com Subject: [PATCH v10 4/4] RISC-V: mm: Document mmap changes Date: Wed, 9 Aug 2023 16:22:04 -0700 Message-ID: <20230809232218.849726-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230809232218.849726-1-charlie@rivosinc.com> References: <20230809232218.849726-1-charlie@rivosinc.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The behavior of mmap is modified with this patch series, so explain the changes to the mmap hint address behavior. Signed-off-by: Charlie Jenkins Reviewed-by: Alexandre Ghiti --- Documentation/riscv/vm-layout.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-lay= out.rst index 5462c84f4723..69ff6da1dbf8 100644 --- a/Documentation/riscv/vm-layout.rst +++ b/Documentation/riscv/vm-layout.rst @@ -133,3 +133,25 @@ RISC-V Linux Kernel SV57 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, B= PF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|___________= _________________________________________________ + + +Userspace VAs +-------------------- +To maintain compatibility with software that relies on the VA space with a +maximum of 48 bits the kernel will, by default, return virtual addresses to +userspace from a 48-bit range (sv48). This default behavior is achieved by +passing 0 into the hint address parameter of mmap. On CPUs with an address= space +smaller than sv48, the CPU maximum supported address space will be the def= ault. + +Software can "opt-in" to receiving VAs from another VA space by providing +a hint address to mmap. A hint address passed to mmap will cause the large= st +address space that fits entirely into the hint to be used, unless there is= no +space left in the address space. If there is no space available in the req= uested +address space, an address in the next smallest available address space wil= l be +returned. + +For example, in order to obtain 48-bit VA space, a hint address greater th= an +:code:`1 << 47` must be provided. Note that this is 47 due to sv48 userspa= ce +ending at :code:`1 << 47` and the addresses beyond this are reserved for t= he +kernel. Similarly, to obtain 57-bit VA space addresses, a hint address gre= ater +than or equal to :code:`1 << 56` must be provided. --=20 2.34.1